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Old 16th July 2012, 06:11 PM   #1
Mull3t is offline Mull3t  United States
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Default How to test a current regulator diode...

Using a DMM I'm getting a reading on my diode test when I switch the red and black probes on a CRD for both sides. Should this be the case? I know a normal diode doesn't have a reading on one side and if it's shorted it will have one on both.
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Old 16th July 2012, 06:43 PM   #2
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The diode test puts a voltage with a high impedance on the DUT, and then shows the DUT voltage on the meter.
To conduct current, the DUT must have a voltage above its turn-on voltage.
For a silicon diode this is about 0.6V.
So if your current source turns on with the voltage that the meter puts out, you will read a non-zero value.
The 'reverse' behaviour of the current diode should be in its data sheet (you DID read the data sheet, didn't you?).

jan didden
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Old 17th July 2012, 01:01 PM   #3
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You could take a battery, say 9 volt if you have one; put the battery, diode and DVM (in the milliamp position) in series and measure the actual current - zero in one direction - "labeled" current in the other.

Charles
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Old 19th July 2012, 03:33 AM   #4
Mull3t is offline Mull3t  United States
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stellavox ~ My DMM unfortunately doesn't have a mA position. But your idea does sound like a good idea.

janneman ~ In other words... if I'm getting a reading from my diode test on my DMM then the device is possibly working. I read the datasheet and I couldn't discern what the behavior of the device should be based on my reading. I did notice that there is "reverse current" under the Ratings category. It reads 50mA. There is no voltage spec. I have very basic knowledge, but want to learn. I did buy a new part so perhaps I'll figure out what readings are normal for this CRD.
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Old 19th July 2012, 08:08 AM   #5
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Just put a resistor in series with the CRD on a battery and measure the voltage drop across the resistor, ohms law gives you the current.

jan
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Old 19th July 2012, 08:58 AM   #6
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Quote:
Originally Posted by Mull3t View Post
stellavox ~ My DMM unfortunately doesn't have a mA position. But your idea does sound like a good idea.

janneman ~ In other words... if I'm getting a reading from my diode test on my DMM then the device is possibly working. I read the datasheet and I couldn't discern what the behavior of the device should be based on my reading. I did notice that there is "reverse current" under the Ratings category. It reads 50mA. There is no voltage spec. I have very basic knowledge, but want to learn. I did buy a new part so perhaps I'll figure out what readings are normal for this CRD.
A DMM without DC current ???? Even the $5 Wallmart cheapies can read current.
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Old 19th July 2012, 09:03 AM   #7
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Quote:
Originally Posted by stellavox View Post
You could take a battery, say 9 volt if you have one; put the battery, diode and DVM (in the milliamp position) in series and measure the actual current - zero in one direction - "labeled" current in the other.
Rectification: labeled current in one direction, toasting the milliammeter and diode in the other
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Old 21st July 2012, 05:37 AM   #8
Mull3t is offline Mull3t  United States
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The DMM certainly can't do amps readings. It's a Fluke 12. I'm going to try and figure the ohms law/voltage drop. I'm sure a 1 ohm resistor would work nicely for this.
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Old 21st July 2012, 08:28 AM   #9
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I'm sure a 1 ohm resistor doesn't work very well.

In the ohms law equation, put in the nominal value of the current diode, like 5mA (as example), for 'I'. Your DMM will comfortably measure, say, 5V, so put that in for 'V'. You want a series resistor that drops around 5V with a 5mA current.
What resistor would that be?

jan
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